collections: Fix broken doc example
collections: Fix broken doc example

PR #32135 was accidentally merged without tests passing, and unfortunately one
of the tests added was broken, so this fixes that.

GBGamer/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust